1. Field of the Invention
The present invention relates to an optical disk drive in which recording and erasing of information, and initialization are performed on an optical disk as a result of light having a waveform of pulse series emitted from a light source being applied on the optical disk. The frequency of the pulse series is higher than the frequency of an information code (recording code) which is recorded on the optical disk. In particular, the present invention relates to a laser-power control device for controlling light-emitting power of a semiconductor laser (laser diode) or the like which is the light source of the optical disk drive.
2. Description of the Related Art
Phase-change-type optical disks such as CD-RW (Compact Disks ReWriteable) are disks on which high-density recording can be performed, and recording and erasing of information and initialization are performed on such disks.
Various methods for recording information on such phase-change-type optical disks have been proposed.
For example, as a recording method which is suitable for use in which overwriting of data is performed on a disk, a recording method (disclosed in Japanese Laid-Open Patent Application No. 63-266632) in which a laser beam having a waveform of a single or a plurality of pulses is applied on a disk so that an amorphous mark is formed on the disk, a recording method (disclosed in Japanese Laid-Open Patent Application No. 1-119921) in which a laser beam having a waveform of high-frequency pulse series is applied on a disk so that an amorphous mark is formed on the disk and a portion of the disk is crystallized, and so forth, have been known.
A recording method for phase-change-type optical disks will now be simply described.
FIGS. 1A and 1B illustrate a principle of the recording method for phase-change-type optical disks. FIG. 1A shows relation between an information code and laser power, and FIG. 1B shows a recorded condition, corresponding to the information code, on a track of the disk. In FIG. 1A, Pp represents a amorphous-phase forming level, Pe represents a crystallizing level and Pr represents a reading level.
In a case where such a phase-change-type optical disk is used, when information is recorded on the disk, a laser spot is applied on the disk, and laser power of a laser beam is changed in accordance with an information code. Thereby, crystallized areas and amorphous marks are formed on a recording film of the disk. Thus, information is recorded on the disk.
Specifically, with reference to FIG. 1A, for a xe2x80x980xe2x80x99 level of the information code, the laser power is caused to be in the crystallizing level Pe. Thereby, portions of the recording film of the disk are crystallized, and, thus, the crystallized areas are formed.
In contrast to this, for a xe2x80x981xe2x80x99 level of the information code, the laser power is changed between the amorphous-phase forming level Pp and the reading level Pr so as to have a waveform of pulse series. Thereby, portions of the recording film of the disk enter an amorphous phase, and, thus, amorphous marks are formed there.
Through such a recording operation, as shown in FIG. 1B, amorphous marks are formed for the xe2x80x981xe2x80x99 level of the information code on the track.
As shown in FIG. 1A, Pp (amorphous-phase forming level) greater than Pe (crystallizing level) greater than Pr (reading level).
Thus, on the phase-change-type optical disk, the crystallized areas for the xe2x80x980xe2x80x99 level of the information code and the amorphous marks for the xe2x80x981xe2x80x99 level of the information code are formed.
For this purpose, the laser power is controlled to have the three levels, that is, the (middle) crystallizing level Pe for the xe2x80x980xe2x80x99 level of the information code, and the (highest) amorphous-phase forming level Pp and the (lowest) recording level Pr for forming the amorphous marks for the xe2x80x981xe2x80x99 level of the information code.
In an optical disk drive, for phase-change-type optical disks such as CD-RW, in which a laser spot having a waveform of high-frequency pulse series is applied on an optical disk, and thus, recording and erasing of information and initialization are performed on the disk, laser power changes at a high frequency.
Therefore, when an emitted-light-intensity detector having a relatively narrow detection frequency band is used, it is difficult to precisely detect emitted-light intensity.
When emitted-light intensity is adjusted by using such imprecisely detected emitted-light intensity, it is difficult to precisely adjust light intensity, and, thereby, it is difficult to stabilize light intensity.
As a result, there is a case where recording or erasing of information, or initialization is performed incompletely.
When using an emitted-light-intensity detector having a wide detection frequency band, expensive light-receiving device and amplifier are needed, and, thereby, the cost of the optical disk drive increases.
In order to eliminate such problems, the inventor of the present invention proposed (in Japanese Laid-Open Patent Application No. 9-171631) an optical disk drive in which emitted-light intensity of a laser diode is stabilized by using an inexpensive and simple arrangement, and, thereby, information recorded on a disk has high reliability.
A laser-power control device in this optical disk drive provides a period during which a laser diode is driven to emit light which does not have a waveform of pulse series. During the period, emitted-light power is detected, and, by using the detected emitted-light power, emitted-light power is controlled.
As a result of emitted-light power being controlled as mentioned above, it is possible to precisely detect emitted-light intensity even by using an emitted-light-intensity detector having a relatively narrow detection frequency band.
However, in detection of emitted-light intensity of the laser diode, the laser diode emits light of recording power (the above-mentioned amorphous-phase forming level Pp) during the period during which the laser diode is driven to emit light which does not have a waveform of pulse series. When light of such high power is applied to an optical disk and emitted-light power is controlled, the optical disk is degraded. When light of the recording power not having a waveform of pulse series is applied on a phase-change-type optical disk, characteristics of the optical disk are remarkably degraded. As a result, recording, reproducing and erasing of information cannot be performed with high reliability.
In order to eliminate this problem, the inventor of the present invention proposed (in Japanese Laid-Open Patent Application No. 9-288840) a laser-power control device in an optical disk drive. In this laser-power control device, setting of laser power having the crystallizing level (middle level) Pe is performed during a period during which an information code has a xe2x80x980xe2x80x99 level and light not having a waveform of pulse series is applied on an optical disk. Thereby, an optimum additional current Ie for the crystallizing level Pe is obtained. An optimum additional current Ip for the amorphous-phase forming level Pp is obtained as a result of the additional current Ie, detected in the period during which the applied light does not have a waveform of a pulse series, being multiplied by a certain coefficient. A base current Ir for the reading level Pr is obtained as a result of a detection output smoothed through a low-pass filter being used, and, thus, an average power level between the highest amorphous-phase forming level Pp and the lowest reading level Pr being detected.
Thus, emitted-light power is controlled by using the output of the low-pass filter during a period during which light has a waveform of pulse series. Thereby, even by using an emitted-light-intensity detector having a relatively narrow detection frequency band and therefore being inexpensive, precise power control can be performed.
As described above, the laser-power control devices in the optical disk drives, by which, even by using an emitted-light-intensity detector having a relatively narrow detection frequency band and therefore being inexpensive, precise power control can be performed, have been known.
However, in the laser-power control device in the optical disk drive (disclosed in the above-mentioned Japanese Laid-Open Patent Application No. 9-171631) in which the period, during which the laser diode is driven to emit light not having a waveform of pulse series, is provided, emitted-light power of the laser diode during this period is detected, and, thereby, emitted-light power is controlled, and in the laser-power control device in the optical disk drive (disclosed in the above-mentioned Japanese Laid-Open Patent Application No. 9-288840) in which the output of the low-pass filter during the period during which emitted-light power has a waveform of pulse series is detected, and, thereby, emitted-light power is controlled, circuits for detecting emitted-light intensity and precisely controlling emitted-light intensity are somewhat complicated.
An object of the present invention is to enable stabilization of emitted-light intensity of a laser diode, and also, to enable high-reliability information recording, by using an emitted-light-intensity detector having a relatively narrow detection frequency band and therefore being inexpensive, in an optical disk drive in which a laser spot having a waveform of pulse series having a frequency higher than the frequency of an information code is applied on an optical disk, and, thereby, recording, reproducing, erasing of information and initialization is performed on the optical disk.
An optical disk drive according to the present invention is provided with a light source (a laser diode 1, shown in FIG. 2) and a light-intensity detecting unit (a photo detector 2, an amplifier 3) which detects intensity of light emitted from the light source, and records an information code on an optical disk by applying light, emitted from the light source, having a waveform of pulse series, on the optical disk. The frequency of the pulse series is higher than the frequency of the information code. The optical disk drive comprises, as a laser-power control device:
a current providing unit (an Ir current source 8) which provides a first current (Ir) to the light source;
a first current adding unit (an Ie current source 7) which provides a second current (Ie) to the light source in addition to the first current;
a second current adding unit (an Ip current source 5) which provides a third current (Ip) to the light source in addition to the first current and the second current;
a first switch unit (an Ie switch 6) which allows the second current to be provided to the light source or prevents the second current from being provided to the light source;
a second switch unit (an Ip switch 4) which allows the third current to be provided to the light source or prevents the third current from being provided to the light source;
a first pulse generator (22) which provides a first on-off control signal (SWe) having a waveform of pulse series to the first switch unit in accordance with the information code;
a second pulse generator (23) which provides a second on-off control signal (SWp) having a waveform of pulse series to the second switch unit in accordance with the information code;
a timing unit (a first timing circuit 24, a first AND gate 19, a second AND gate 20) which generates a timing signal (SHr) for preventing the first and second on-off control signals (SWe, SWp) from being provided to the first switch unit and the second switch unit, respectively, during a predetermined period;
a first sample-and-hold unit (a first sample-and-hold circuit 17) which samples and holds output (Vd) of the light-intensity detecting unit during the period during which the timing signal is generated;
a second sample-and-hold unit (a second sample-and-hold circuit 18) which samples and holds the output of the light-intensity detecting unit during a period during which the first on-off control signal is in a first level (H) and the second on-off control signal is in a second level (L);
a first adjusting unit (a first comparator 13, a micro controller 12, a first D-A converter 9) which adjusts the first current depending on output of the first sample-and-hold unit;
a second adjusting unit (a second comparator 14, the micro controller 12, a second D-A converter 10) which adjusts the second current depending on output of the second sample-and-hold unit; and
a third adjusting unit (the second comparator 14, the micro controller 12, a third D-A converter 11) which adjusts the third current depending on the output of the second sample-and-hold unit.
In this arrangement, when the laser diode 1 is caused to generate the crystallizing level Pe, the current Ie for the crystallizing level Pe is added to the current Ir for the reading level Pr. When the laser diode 1 is caused to generates the amorphous-phase forming level Pp, the current Ip for the amorphous-phase forming level Pp is added to the current Ir for the reading level Ir and the current Ie for the crystallizing level Pe.
During a period during which the information code is in the xe2x80x980xe2x80x99 level and the laser diode 1 is caused to generate the crystallizing level Pe, the laser power of the laser diode 1 is in the crystallizing level Pe in a condition in which the laser power does not have a waveform of pulse series. Therefore, as a result of the emitted-light-intensity detection voltage Vd being sampled during the period, it is possible to precisely detect the crystallizing level Pe.
Further, the laser power of the laser diode 1 is caused to be in the reading level Pr, in a condition in which the laser power does not have a waveform of pulse series, during the above-mentioned predetermined period, every predetermined time. Therefore, as a result of the emitted-light-intensity detection voltage Vd being sampled during the predetermined period, it is possible to precisely detect the reading level Pr.
Then, based on the precisely detected respective levels (Pe and Pr), the currents Ir and Ie which are provided to the laser diode 1 are adjusted.
Therefore, even in a case where the detection frequency bands of the photo detector 2 and the amplifier 3 are relatively narrow, it is possible to precisely detect the laser power having the crystallizing level Pe and the laser power having the reading level.
As a result, it is possible to precisely adjust the laser power having the crystallizing level Pe and the laser power having the reading level Pr to be in desired levels, respectively. Thereby, it is possible to stabilize the emitted-light intensity, and, thereby, it is possible to improve reliability of information recorded on an optical disk.
The first adjusting unit may compare the level of the output of the first sample-and-hold unit with a first predetermined level (a predetermined voltage Tr output from a fifth D-A converter 16), and control the first current depending on the comparison result; and
the second adjusting unit may compare the level of the output of the second sample-and-hold unit with a second predetermined level (a predetermined voltage Te output from a fourth D-A converter 15), and control the second current depending on the comparison result.
The third adjusting unit may control the third current so that the third current has the value obtained as a result of the value of the second current which is controlled by the second adjusting unit being multiplied by a predetermined coefficient.
In this arrangement, the ratio of the third current (the current Ip for the amorphous-phase forming level Pp) to the second current (the current Ie for the crystallizing level Pe) is predetermined to be the value such that a desired amorphous-phase forming level Pp can be obtained by using the value.
In this case, although the laser power having the amorphous-phase forming level Pp is not directly detected, the current Ip obtained as a result of the adjusted current Ie being multiplied by the predetermined coefficient is provided.
As a result, it is further possible to precisely adjust the amorphous-phase forming level Pp to be a desired level.
The second sample-and-hold unit may sample and hold the output of the light-intensity detecting unit during a period during which the first on-off control signal is in the first level and the second on-off control signal is in the second level, which period is longer than a predetermined time.
In this arrangement, because a sampling timing signal SHe is in the xe2x80x98Hxe2x80x99 level only in a case where a period during which the xe2x80x980xe2x80x99 level of the information code continues is longer than the predetermined time so that the emitted-light-intensity detection voltage Vd output from the amplifier 3 sufficiently stabilizes, the second sample-and-hold unit 18 can sample the detection voltage corresponding to the crystallizing level Pe.
As a result, the emitted-light-intensity detection voltage Vd is sampled only during the period during which the xe2x80x980xe2x80x99 level of the information code continues and the laser power does not have a waveform of pulse series, which period is longer than the predetermined time. That is, the sampling timing signal is in the xe2x80x98Hxe2x80x99 level through the period in which the emitted-light-intensity detection voltage Vd sufficiently stabilizes. As a result, it is possible to detect the crystallizing level Pe further precisely.
The second sample-and-hold unit may sample and hold the output of the light-intensity detecting unit during a period during which the first on-off control signal is in the first level and the second on-off control signal is in the second level, which period is corresponding to the longest inverting time of the information code.
In this arrangement, because the sampling timing signal SHe is in the xe2x80x98Hxe2x80x99 level only during a period during which the xe2x80x980xe2x80x99 level of the information code continues, which period is corresponding to the longest inverting interval, so that the emitted-light-intensity detection voltage Vd output from the amplifier 3 sufficiently stabilizes, the second sample-and-hold unit 18 can sample the detection voltage corresponding to the crystallizing level Pe.
As a result, the emitted-light-intensity detection voltage Vd is sampled only during a period during which the xe2x80x980xe2x80x99 level of the information code continues and the laser power does not have a waveform of pulse series, which period is corresponding to the longest inverting interval. That is, the sampling timing signal is in the xe2x80x98Hxe2x80x99 level through the period in which the emitted-light-intensity detection voltage Vd sufficiently stabilizes. As a result, it is possible to detect the crystallizing level Pe further precisely.
Other objects and further features of the present invention will become more apparent from the following detailed descriptions when read in conjunction with the accompanying drawings.